DESCRIPTION (Adapted from applicant's description): The general purpose of this proposal is to examine the behavioral and neurobiological consequences of development exposure to oxytocin (OT). Changes in OT are particularly likely to occur around the time of birth, and the proposed hypothesis is that the consequences of exposure to OT during the neonatal period may be long-lasting, producing functional changes in adulthood. This hypothesis will be examined in the context of female reproductive behaviors, which are particularly sensitive to the effects of OT and steroid hormones and their interactions. Developmental exposure to OT also may affect CNS levels of OT receptors, which could in turn alter sensitivity to OT in adulthood. In addition to behavioral assessments, the investigator proposes using neuroanatomical methods to index, as a function of neonatal manipulations of OT, both OT and OT receptors in adulthood. Developmental exposure to OT may affect adult behavior by influencing steroid sensitivity; this hypothesis will be examined by the measurement of estrogen or progesterone receptors. In addition, the effects of development exposure to OT on arginine vasopressin (AVP) and its receptor (V1a) will be examined; AVP is closely related to OT in both structure and function. Finally, a nonspecific marker of cellular activity (c-Fos) will be used to index the capacity of animals with different developmental histories to respond to adult treatment with estrogen or OT. The behavioral effects of both OT and estrogen can be species specific; for this reason two animal models (prairie voles and rats) have been selected, taking into account the advantages of each for examining the behavioral effects of both OT and steroid hormones and their interactions.